Process of dewaxing hydrocarbon oils



Patented Oct. 18, 1938 UNITED STATES PATENT OFFICE Paul D. Barton, Scarsdale, N. Y., assignor, by

mesne assignments, to Sun Oil Company, Philadelphia, Pa., a corporation of New Jersey Application January 22, 1934, Serial No. 707,637

Claims.

My invention relates to a dewaxing process and more particularly to a multi-stage dewaxing process utilizing an excess of a solvent diluent in the first stage.

Generally speaking, in a process for dewaxing hydrocarbon oils containing a large percentage of paraiiin Wax which utilizes a normally gaseous liquifled hydrocarbon solvent such as propane to secure dilution, chilling and resultant crystallization of the wax, considerable difficulty has been experienced in transferring through pumps, pipe lines and other pieces of equipment associated with the process, the wax-bearing oil diluted in the customary manner. The viscosity of oil sol- Vent mixture under the usual dilution conditions of, for example, one part oil and three parts propane is such as to preclude a satisfactory commercial rate of dewaxing in a continuous process. It is an object of my invention to provide a process for dewaxing hydrocarbon oils containing a. high percentage of wax not readily removed by a continuous process involving low dilution of the oil with a hydrocarbon solvent because of mechanical difficulties incident to pumping and filtration.

Another object of my invention is to provide a multi-stage dewaxing process in which a hydrocarbon oil bearing a high percentage of wax is highly diluted with a hydrocarbon solvent, chilled and partially dewaxed, the concentration of the partially dewaxed oil in the solvent then being increased by denuding the mixture of some solvent, the oil again chilled to a lower wax precipitating temperature and additional wax removed to givethe desired low cold test oil.

Other and further objects of my invention will be seen from the following description.

The accompanying drawing which forms part of the instant specification and is to be read in conjunction therewith is a schematic drawing of one form of apparatus capable of carrying out the process of my invention.

In general, I mix a stock bearing a high percentage of wax with a liquefied, normally gaseous hydrocarbon solvent such as propane, for example,

under such conditions as will secure an initial dilution sufficient to obtain a solution and permit more ready transfer of the solution to a second mixing chamber where a. large amount of solvent diluent which has been separately chilled to a predetermined low wax precipitating temperature is mixed with the first oil diluent solution. This highly diluted and chilled solution is held under pressure in a separating tank which permits a preliminary settling of the larger and heavier Wax crystals solidified and from which separator a selected upper portion of the oil from which some of the wax has been crystallized and precipitated by the chilled solvent, is removed, filtered, and then completely or partially denuded of the solvent diluent before subsequent further dewaxing. The removal of a predetermined amount of the solvent at this point is necessary before further dewaxing is attempted in order that the proper concentration of the oil in the 10 diluent for most favorable wax crystallization conditions may be secured. It may be desirable as an alternative to remove all of the initial solvent at this point and utilize a different solvent of higher vapor pressure for the subsequent furl5 ther dewaxing operation. The remaining oil wax slurry from the separating tank is passed through filters, the filtrate from which is combined with the partially dewaxed undenuded oil while the slurry from the filters is denuded of this propane 20 solvent and passed to storage as first wax or petrolatum.

The partially dewaxed oil with solvent diluent for the desired concentration, is cooled by indirect heat exchange from surrounding evaporating 25` propane and passed into a crystallizer tank where evaporation is prevented by pressure of a lighter gas and where the time, temperature conditions necessary for crystallization are maintained. This process of chilling and crystallizing under 30 pressure is carried on through a number of steps, the temperature and pressure decreasing and the amount of crystallized wax increasing in each step. The final desired crystal formation is achieved in the last crystallizer Where the diluent 35` is caused to evaporate either from direct pressure relief or as the result of a light gas partial pressure effect to secure the proper oil concentration in the solvent. Some temperature reduction may occur as the result of incidental auto-refrigera- 40- tion in the last crystallizer though indirect heat exchange may be used. The oil, bearing the crystallized wax, is then passed through a series of filters of desired type, the filtrate of dewaxed oil being taken off, denuded of diluent in a distilla- 45 l itial oil propane solution, thus inhibiting auto- 55! refrigeration by evaporation of a part of the diluent. The gas serving as a pressure medium on this settling tank and on the crystallizers in the second stage of crystallization is selected from 5 a gas having relatively 10W solubility in the oilpropane mixture. This gas may be, for example, carbon dioxide or methane. The latter is especially desirable for securing propane evaporation by partial'pressure reduction inthe later crystallizers.

Referring now more particularly to the drawing, a wax-bearing stock from tank I ispumped through a line 2 by pump 3 toa mixing chamber 4 where it is mixed with a normally gaseous liquified hydrocarbon solvent diluent such as propane or the like, taken from tank 5 and pumped through the line 5 by pump 1. The oil diluent solution is transferred through-the line 8 to a second mixing chamber 9. Diluent is Withdrawn from the tank 5 through the line ||l and -injected into thechiller il Where it is cooled as a-result of evaporationof a portion of the diluent, the gas escaping throughjline I2 having a pressure relief valve i3.

I5 to the` mixing chamber 9. The highly diluted oil diluent solution from the chamber 9 passes through the line |6.to a separating tank |1 having a series of baiiie plates .larranged to miniofimize agitation resulting. from eddy currents set up in the tank. y Y

A compressor I9 serves to pump a light gas such as carbon dioxide or methane to tank |9atted with drain |912. Gas from tank |9a passes nthrough the line 29 and branch line 2| to the separating tank I1 at a pressure suicient to prevent evaporation ofthe diluent in the tank. As

'a result of the interchange of sensible heat between the oil and subcooled diluent, some of the 40. Wax in the oil is crystallized, settles andincreases the percentage of Wax crystals in the lower portion of the oil solution in tank |1. A layer of partiallyl dewaxed oil is Withdrawn from the upper level of the tank through the line 22 and injected intoVv a lter unit of the desired type as 23. A ltrate of partiallyrdewaxed oil -is Withdrawn from the filter `unit 23 `through Yline 24 connected to a filtrate main 25 passing to an accumulator tank 26. The oil Wax slurry in the -lower portion of the lter unit 23 vis Withdrawn through lthe line 21 and combines With oil Wax slurry being withdrawn from the tankl1 through the -liner 28. This-slurry is passed through the line 29 to thelter unit 30 from which filtrate ,may be withdrawn through the line 3| and slurry through the line 32. The slurry is further ltered in the lilter unit 33, filtrate being Withdrawn through the line 34and slurry through the line 35. The ltrate being Withdrawn from the units 60. through the lines v3| and 34 is passed into the main 25 connecting With the accumulator tank 25. Valves 36 and 31 are provided in the line` 28 permitting the units 38 and 33 to be operated in series or cut out asdesired.

The partially dewaxed oil is Withdrawn from the tank 26 through the line 38 having a pump 39 passed through the heat exchanger 48 to a distillation ,unit-4| Where the diluent is Wholly or partially distilled oiand collected in the main 7013.42. `The partially `dewaxed oilv denuded of its diluent is then sent through the liner 43 to a. tank 44. Alternatively, the partially denuded oil may be introducedgdirectly to the rst indirect solution chiller 54 through a. by pass 43a, controlled 75;;by. valve43b. The Wax slurryfrom the filter ltallizers 552,` 553, 554' arranged in series.

` The chilled diluentfrom the chiller 25 ,II is pumped through a line I4 having a pump unit 33 is withdrawn through the line 35 connecting to the line 45 which passes to a distillation unit 46 serving to remove the diluent which passes oiic through the line 42 While the denuded Wax or petrolatum passes 01T through the line 41 to storage.

The partially dewaxed oil is passed to a mixing chamber 59, either from tank 44 or through line 43a. Diluent Which may be the same or have a higher vapor pressure is withdrawn from the tank 5 (or a separate tank, not shown) through the-line 5| having apump 52 and mixed with the l oil in the mixing chamber 59 in the desired ratio to give the required higher oil concentration for loW cold test oil product. The oil diluent mixture passes through line 53 and heat exchanger 541,

to the crystallizer 551. The oil Withdrawn from .the crystallizer 551 passes through lines 53 and a series of heat exchangers 542, 543, 544, and crys- Liquid diluent is, introduced to each of the heat exchangers 54 through the lines 55,` permitted. to evaporate and escape through the lines 51 having pressure relief valves 58. These lines are connected to a main 59 running to the inlet side of the pump of the compressor Si]V to the outlet of which is connected a line 6| passing -through heat exchanger 62 to the diluentvsupply tank 5. Pressure is maintained on each of the crystallizers by compressed light gas injected through the lines 53. Branch lines may be provided for injecting light gas directly into the oil diluentH solution if desired to secure diluent evaporation by partial pressure eiect in the last crystallizer. A series of escape lines 54 provided with pressure relief valves 55 yare connected toa common main 66 which returns the gaseous diluent to the intake side of the compressor i9.

Each of the crystallizers 551, 552, 553, 554, is provided with liquid level controls 911, 912, 913, 914, respectively, for operating the valves 981, 982, 983, 984, respectively, for controlling the pressure and iiow of the liquid into the respective crystallizers 551, 552, 553, and 554.

The oil bearing the crystallized Wax is Withdrawn from the last crystallizer 554 through the line 61 having a pump 98. Branch lines 69, 10,

1| and 12 connect the linel S1 with the filter units Y 13,14, 15 and 16. Withdrawal linesf11, 18, 19 and 89 connect the bottom of the lter units with the line 51 which is also provided with the valvesy 8h82,Y 83 and 84 which permit the lter units to be operated eitherin series or cut out as desired. The filtrate from the lter units is removed through the line 85 and passed into a distillation unit 86 from which the diluent is removed through the lines 86a and 42, and the iinished dewaxed oil removed through the line 81. It will be understood that if a diierent diluent from that in tank 5 is used, line 86a will return the same to its oWn tank (not shown). rlhe wax-diluent slurry from the iilter unit is passed through the line 88a to Vthe tank 88 from which it is removed through a line 89 having a pump 90 and sent to a distillation unit 9| from which the diluent is. removed through the line 42 and the wax or petrolatum removed through the line 92. The accumulated diluent` from the` distillation coY units 44,46, 9| and 86 maybe collected in the line s 42 and passed through-a branch line 93, cooled' in heat exchanger 94, to an accumulator fromY which it is returned through the line 96v and heat exchanger 49 to the diluent supply tankr5.

, is as follows:

The wax-bearing stock and` diluent such as propane from tanks I and 5 respectively are combined in the mixing chamber 4 in ratio of about one to three parts by volume. This solution, as a result of sensible heat exchange (and the operation of an external Water cooled heat exchange means, if desired, (not shown) will be cooled to a temperature of about '15 F. Diluent withdrawn from the tank 5 is sub-cooled to 45 F., for example, in the chiller II by evaporation of a portion thereof, the sub-cooled diluent then being mixed with the first oil diluent solution in the chamber 9 in a ratio of two to twenty, for example. The entire solution now reaches a temperature of about 30 F. in the separating chamber I1 where the diluent is kept from evaporating as a result of the restraining action of the carbon dioxide or methane at a pressure which may be as high as 200# maintained by the compressor I9 on the separating tank I1. I'here will be a slight rise in temp- 'erature of the filtrate from the filter units 23,

30 and 33, the partially dewaxed oil in the accumulator 2B being, for example, in the neighborhood of 25 F. This oil, after passage under pressure throughthe heat exchanger 40 and distillation unit 4I, will be at a temperature governed by available cooling water, say about F. and at a pressure in the neighborhood of 175#. The oil is either completely denuded of `diluent in distillation unit 4I and then accumulated prior to redilution with a diluent of higher vapor pressure, or sufiicient diluent is removed to secure a concentration of the oil-diluent ratio which will insure proper crystal growth in the subsequent dewaxing step.

The oil, if completely denuded of diluent is withdrawn from the accumulator 44 and mixed with a different diluent from the tank 5 or a separate tank (not shown) in a ratio of substantially one part oil to three parts of diluent by volume. The temperature of the mixture will be around 70 F. and this will be cooled in passing through the indirect solution cooler 541 to a temperature of +30 F. as a result of the evaporation of diluent in the indirect solution cooler 541, which diluent will be at a temperature of from 0 to 15 F. The wax oil solution from the first crystallizer 55, will be cooled in passing through the second indirect solution cooler 542 to a temperature of 0 F., in passing through the third indirect solution cooler 543 to a temperature of 10 F., and in passing through the fourth solution cooler 544 to a temperature of 20 F. Each of the crystallizers 55 is maintained under pressure by the gas from tank I9a to prevent evaporation of the diluent in the crystallizers. This pressure may be less in each crystallizer due to the progressively decreasing temperature of the mixtures. For example, the first crystallizer 551 may be at 200# pressure, the second 552 at 150# pressure and the third 553 at 100# pressure. The fourth crystallizer 554 will be at atmospheric pressure and diluent will be permitted to evaporate from the mixture either by the reduction to atmospheric pressure or as the result of injected light gas to secure the desired concentration of mother liquor giving favorable crystal growth. The oil-wax diluent mixture removed from the last crystallizer 55 is filtered in the selected filter units, the ltrate removed through line being denuded of its diluent in the distillation unit 86 and sent to storage as finished dewaxed oil through the line 81. The slurry from units 13-16 is accumulated in tank 88 and pumped through line 89 to distillation unit 9| where the diluent is removed. The petrolatum is sent to storage through line 92.

It will be understood that certain features and subcombinations are of utility and may be ernployed with reference to other features and subcombinations. This is contemplated by and is within the scope of my claims. It is further obvious that various changes may be made in details within the scope of my claims without departing from the spirit of my invention. It is, therefore, to be understood that my invention is not to be limited to the specific details shown and described.

Having thus described my invention, what I claim is:

1. A process for dewaxing hydrocarbon oils comprising diluting the oil with a hydrocarbon solvent, chilling the oil-diluent solution to secure partial crystallization of the wax, separating the wax from the oil, denuding the partially dewaxed oil of the solvent, diluting the partially dewaxed oil with a different hydrocarbon solvent of higher vapor pressure than said rst solvent, chilling the oil-diluent solution to crystallize a further portion of the wax and removing the wax from the oil.

2. A process for dewaxing hydrocarbon oils comprising diluting the oil with a hydrocarbon solvent, further diluting the oil-solvent solution with a chilled hydrocarbon solvent to secure crystallization of a portion of the contained wax, separating the wax from a selected portion of the oil, denuding the partially dewaxed oil of the hydrocarbon solvent, diluting the partially dewaxed oil with a different hydrocarbon solvent of higher vapor pressure than said first solvent, chilling the oil-.diluent solution to a. temperature lower than that achieved in the first stage of dewaxing and removing the wax from the oil.

3. A process for dewaxing hydrocarbon oils comprising diluting the oil with a solvent diluent, chilling a solvent diluent by auto-refrigeration, further diluting the oil-diluent solution with the chilled diluent, introducing the highly diluted chilled solution to a separating stage, maintaining a pressure in the separating stage with a gas substantially insoluble in the solution sufiicient to prevent evaporation of the diluent, removing a selected portion of solution from the separating stage and introducing it to a filtering stage, removing the iiltrate and partially denuding it of the solvent diluent in a distillation stage, to secure a much higher oil concentration in the solution, progressively chilling the solution and crystallizing the Wax in a series of heat exchange and time crystallization stages while maintaining a super atmospheric pressure in the crystallizing stages with a gas substantially insoluble in the solution, evaporating the diluent from the mixture in the last stage of crystallization to secure the desired concentration of oil, removing the mixture from the crystallizer and introducing it to a filtration stage, removing the filtrate and denuding the wax free oil of the diluent in a distillation stage.

4. The process of claim 3 in which the first oil-diluent solution is in substantially the ratio of one to three parts by volume, in which the second oil-diluent solution is in the ratio of substantially two to twenty parts by volume and in which the partially denuded oil-diluent solution is in the ratio of substantially one to three parts by volume.

5. A process of dewaxing hydrocarbon oils comprising preparing a highlyidiluted oilsoln vent solution, chilling the solution, ltering the solution to secure ,a partially` devvaxed4 Cil diluent filtrate, removing .a portion ofthe diluent :from the ltrate, chilling the: iltratesdiluent solution to a vp1"e.'etermined temperature lower than said rst chilling temperature by lindirect heat exchange While maintaining a,V super ya1:- 

